1. Field of the Invention
This invention relates to electrolytic devices such as batteries, and more particularly, to closure constructions about the terminal posts for such devices.
2. Description of the Prior Art
Electrolytic devices such as batteries ordinarily include a housing serving as containers for internally disposed electrodes disposed electrodes and the electrolyte. A pair of terminal posts generally extend from the electrodes within the container through openings in a cover which is provided as the top surface of the housing. The electrolyte, which is generally a liquid or a paste-like substance, tends to move along the surface of the terminal ports lying between the housing and posts. In order to prevent continued loss of the electrolyte due to leakage and evaporation, the container is preferably sealed and often includes sealing the cover to the casing, and to the terminal posts.
A particular vexatious problem is the electrolyte leakage which occurs in close proximity to the terminal posts. The combination of various factors such as spacing that occurs between posts and covers, the low viscosity of electrolyte, vibration of the battery due to the associated operating equipment and pressure of generated gas within the battery and capillary action of liquids all combine to cause the electrolyte to move upward along the posts. The consequences of such electrolyte leakage are two-fold. First, leakage tends to reduce the working efficiency of a battery. Second, electrolyte leakage, due to the reactivity of the electrolyte constituents can corrode expensive equipment in close proximity to the battery or the battery itself.
The prior art is replete with examples of various attempts to prevent egress of electrolyte along the terminal posts. Most prior attempts require the use of specialized sealing materials, unusual geometry at the interface of the terminal posts and container cover, or combination thereof. For example, U.S. Pat. No. 4,572,877 issued Feb. 25, 1986 to Botos discloses an hermetic seal for an electrochemical cell. The seal disclosed there includes an electrical insulating material, such as glass, which is fused in the passageway between the terminal and the battery housing in an attempt to prevent electrolyte leakage through the housing opening. While devices such as this generally decrease the amount of electrolyte leakage, the glass or ceramic used often suffers from chemical attack. This in turn leads to the degredation of the seal and subsequent operating effeciency reduction or even failure of the battery. Failure here may be due to the formation of a conductive layer on the glass or to the electrolyte leakage itself.
Another type of seal, commonly employed in alkaline batteries, is a crimp seal. In this type of seal, sealing material is interposed between an upright, cylindrical flange, sometime part flange of the cover itself, and terminal post. A cap seals the battery by fitting over the flange. The sealing material, generally comprises a polymeric material and is utilized to prevent electrolyte leakage. One form of a crimp seal is shown in U.S. Pat. No. 2,665,329 issued Jan. 5, 1954 to Brenner which discloses, in one embodiment, a container which is deformed inwardly by a metallic ring with the container in turn compressing a rubber sealing material against a terminal post.
U.S. Pat. No. 4,559,283 issued Dec. 17, 1985 to Kruger et al. discloses another type of crimp seal that includes a heat recoverable sealing ring. The ring is compressed against the metallic flange of the battery casing which, in turn, compresses a polymeric sealing substance against the terminal post. The heat recoverable sealing ring is disclosed as being able to endure greater compressive forces thus reducing the amount of spring back.
Still another type of seal, disclosed in U.S. Pat. No. 3,051,769 issued Aug. 28, 1962 to J. F. Jammet, comprises a plastic casing having an inward projection at the terminal site pressed against the terminal by use of a zinc rim positioned within the battery cell. The zinc rim provides inward pressure on the inwardly directed flange causing it to bear tightly against the terminal. It is noteworthy that the zinc rim is exposed to corrosive effects of the electrolyte and must be covered with a protective coating material. U.S. Pat. No. 3,433,681 issued Mar. 18, 1969 to J. F. Jammet discloses a similar type design wherein the terminal is provided with grooves which engage the casing and aid in ensuring the tightness of the seal. Additionally, it is necessary to improve the tightness of the seal by coating a layer of wax over the top of the terminal.